Hello All, Long time lurker, first time poster. I'm hoping another geo professional or informed homeowner will be able to give me some insight on their experience/success/problems/performance concerning using a directional horizontal boring rig to install the HX field. My problem is three-fold; 1) The geo drillers prices have shot up in my area, 2) None have been very reliable, 3) The rigs and crews leave a big mess for us to clean up after. I am unwilling to spend two years as an apprentice driller (not that anyone would hire a worn-out HVAC business owner) just to become licensed to drill a vertical hole and thought about using a directional horizontal rig. The soils here are conducive to using a directional drill and I will be able to schedule the work better and hopefully control costs and cleanup. Does anyone have experience using this type of technology for geo and did it work satisfactorily? I'm leaning toward the DitchWitch JT1220 if it seems that it will work. The company is willing to send a machine to a job and demo it but I'd like to get some feedback before I waste time and money. Additionally I realize I will need to grout the hole and plan on pulling the tremie pipe along with the HX piping to make sure there are no voids. I have never dug a horizontal field because the soil here is mostly black-land clay and during droughts the ground has dried out to a depth of >6ft. All my installs so far have been good using vertical holes and I don't want to get a bad rep if we have another serious drought and I lose heat conductivity. I'd plan on the directional boring depth to be an average of 10-15'.
GeoPro, I don't work in the geothermal field, but I'm very interested in learning as much about it as possible. I came across a company in Germany that installs borehole heat exchangers (geothermal heating and cooling systems). Very innovative approach using horizontal directional drilling; it might give you some inspiration. See installation video: Tracto-Technik TV
It's common enough in the utility industry - just look up DitchWitch. It just hasn't spilled over in to the geo market as much - partly because an excavator is always readily available for horizontals.
Directional boring The company I work for does a lot of geo loops with directional boring machines in Northern Wisconsin. We use vermeer drills, the 36-50 model is the best suited for the job because it will bore quickly. The rule of thumb of 200' bore per ton has been working out quite well. The usual bore depth we use is 20', that will get the loop into normally saturated soils. We have installed over 100 loop fields in the last 3 years and have not had one that did not perform as calculated. Unlike backhoes, boring machines like wet conditions and low areas. I can put a loop into the soil that works the best with minimal mess. We usually bore a 6 ton loop in a day in good boring conditions. The cost is about 70% of vertical drilling and works as well in most cases. Dr.Bob
Outstanding! Directional has been done comercialy but slow to catch on in a residential setting. What is your cost per foot to bore? Are you grouting during pull back? If so are you using betonite at what solids content? Or are you using graphite? Is there a rock formation below the overburden that makes vertical 70% more?
directional boring In answer to waterpirate, grouting is not as critical as vertical boring because we do not cross aquafers so sealing of the borehole is not that important. We do use bentonite for a drilling fluid and pump additional bentonite into the bore during pullback to help fill the hole. Soil types dictate the amount of drilling fluid necessary. Gravity helps to collapse the bore hole to further tighten the soil contact with the soil. The heat exchange tubes are pulled back with the drill rod. 300' loops seem to work the best, giving 1 1/2 ton per bore, a 6 ton system works well with 4 loops. about $1700 per ton is where we are at for a 6 ton system, complete, manifolded, pressure tested and purged, ready to go into the house, All excavation is restored, blackdirted and reseeded with grass. Larger systems are less per ton Every job is bid seperately some are easy, some are not. Dr.Bob
Thanks for the info Drbob. I have been discouraged by the distributor for horizontal excavation installations here since three years ago during a severe drought, our blackland clay soils opened up to depths up to 8 ft. A horizontal bore seemed like it should work here but everyone has been resigned to hiring the vertical drilling companies. How deep do you dig your manifold trench?
Yes, please elaborate, Dr. Bob. I would love to hear this. How do you get pipes horizontal at 20 ft? And how do you pull the tubes through?
Horizontal directional boring machines have been used for years placing underground utilities (gas,power,telephone,sewer, etc.) The drill enters the ground at about a 25 degree down angle, upon reaching the desired bore depth the drill can be turned to travel horizontally, upon reaching the desired bore length the drill can be turned to go back up and exit the ground. The pipes are then hooked to the drill head and pulled back to the machine. The only ground scars left are where the boring machine was set up and a small 3" hole where the drill exited the ground. We normally manifold in the area where the drill was set up. This requires a backhoe to expose the pipes to about the 5' depth the pipes are manifolded there to header pipes which go to the building. If the machine can be set up close enough to the building then we manifold inside the building which is the best case possible, eliminating many fusion joints being buried underground. The disadvantage to horizontal boring is you need a large area for the heat field, an acre or more. The most cost effective bore is 300' in length. A 300 foot loop (600' pipe) normally yields 1 1/2 tons of heat. Drilling in rocky ground is also not cost effective. It is doable but not cost effective. If your lot size is too small vertical drilling is normally the only option due to the space requirements. I hope this helps explain things a little clearer. Horizontal boring is an option, not the only option, sometimes it is the most cost effective, sometimes it is not. Dr.Bob
Directional Boring Here is an interesting report on HDD from Arizona State: HDD The jury is still out for me. If you are drilling to pull (2) 3/4" pipes through, how big is the bore hole? How can you be sure that the grouting has been successful? We have seen a couple of these systems fail. If the pipes are not able to get down to our water table or at least damp soil, they do not perform. The length of time required to bore does not compare to open trenching. Here in Indiana, there is current legislature on the books to require HDD contractors to have a well-drilling license. It is remarkable technology and we stand by and wait for it's evolution. It does have some very good points and I am still open minded as this evolves. Just my $.02
Hdd licensure? I believe that requiring a HDD driller to obtain any liscense for anything except to do business is a very odd request. I also think that the depth of the hdd bore is only limited by money and the size of the machine. Hdd has been doing infrastructure work under all sorts of bodies of water for a long time, so getting an hdd loop into the water table is about the economics. I am sure that there are plenty of places where a hdd loop into a water table would be cheaper than open excavation or vertical. I have read where hdd was chosen as a means to an end. Specifically providing loops where a lot of money had allready been spent on athletic feilds prior to the geo being installed.
Drilling Liscense I don't think it's odd to require a license because at times, some contractors are in the aquifer in some areas. I don't agree with it, but I see the logic. How would that be any different than needing a license to install vertical loops? Just curious.
well cwis. We have put in over 50 systems with directional boring, not a one has failed. The typical bore depth we put in is 20' the reason is that the biggest excavotar we have will dig to 23' in case of a broken drill stem we can still retrieve the drill head. Drill heads are about $4000.00 We only needed to dig up one so far. Directional boring has to be done right. If done wrong it will not perform. Any other method has to be done right or it will fail also. I turn down a lot of jobs if I do not think it will perform. Grouting is important for vertical bores to protect from cross contaminating two or more aquafers passed through during the drill. With horizontal boring we do not cross two aquifers. We can place a 6 ton system in an 8 hour day. Cant do that with an open excavated loop. We have 20+ backhoes and 5 directional drilling machines. Dr.Bob
Well Ciws? Well Dr. Bob. You are right in mentioning 1 of the reasons grouting is important, and yes it is important for cross contamination. That is a very good reason, but another reason that was not mentioned is the thermal conductivity that grouting promotes. That is the only reason on using thermally enhanced grout. Is it not necessary to grout the HDD bores? Again, I am not saying HDD does not work, but it does not work in all cases. No single method works in all cases. I have just (2) backhoes, (1) excavator and (1) trencher to know that... HDD is a very viable and exciting technology that we have been following for years. I am just saying it needs to be looked at all angles and as not the answer-all. I am glad you have installed over 50 systems with HDD technology with no failures. I hope this continues for you and you are able to educate the rest of us as time goes on.
check out HDDforums.com • Index page for more information directly related to horizontal directional drilling, as well as equipment repairs for Vermeer, Ditch Witch, American Auger, Case, Astec and more.
HDD Animation Here is a link to the video I usually show during my trainings: YouTube - Directional Drilling Rig‏ It gives you an idea of how they steer with those machines. In geothermal drilling, when they pull the drill stem back out of the bore (with the reamer attached), they'll pull the u-bend and tremie back with it to complete the bore installation. While aquifers aren't usually penetrated during horizontal boring, grouting is just as important in this application as it is in vertical. While some soils will collapse completely around the u-bend piping in the bore, some soils will not. Grouting is the only way to guarantee the contact between the pipe and the earth that is necessary for proper heat transfer.
